The conversion of hydrocarbons to hydrogen and carbon monoxide containing gases is well known in the art. Examples of such processes include catalytic steam reforming, auto-thermal catalytic reforming, catalytic partial oxidation and non-catalytic partial oxidation. Each of these processes has advantages and disadvantages and produces various ratios of hydrogen and carbon monoxide, also known together as synthesis gas.
Partial oxidation processes are also well known and the art is replete with various catalytic and non catalytic processes. Catalytic partial oxidation is an exothermic reaction wherein a hydrocarbon gas, such as methane, and an oxygen-containing gas, such as air, is contacted with a catalyst at elevated temperatures to produce a reaction product containing high concentrations of hydrogen and carbon monoxide. The catalysts used in these processes are typically noble metals, such as platinum or rhodium, and other transition metals, such as nickel on a suitable support.
Partial oxidation processes convert hydrocarbon-containing gases, such as natural gas, to hydrogen, carbon monoxide and other trace components such as carbon dioxide and water. The process is typically carried out by injecting preheated hydrocarbons and an oxygen-containing gas into a combustion chamber where oxidation of the hydrocarbons occurs with less than stoichiometric amounts of oxygen for complete combustion. This reaction is conducted at very high temperatures, such as in excess of 700° C. and often in excess of 1,000° C., and pressures up to 150 atmospheres. In some reactions, steam or carbon dioxide can also be injected into the combustion chamber to modify the synthesis gas product and to adjust the ratio of hydrogen to carbon monoxide.
More recently, partial oxidation processes have been disclosed in which the hydrocarbon gas is contacted with the oxygen-containing gas at high space velocities in the presence of a catalyst such as a metal deposited on a ceramic foam (monolith) support. The monolith supports are impregnated with a noble metal such as platinum, palladium or rhodium, or other transition metals such as nickel, cobalt, chromium and the like. Typically, these monolith supports are prepared from solid refractory or ceramic materials such as alumina, zirconia, magnesia and the like. During operation of these reactions, the hydrocarbon feed gases and oxygen-containing gases are initially contacted with the metal catalyst at temperatures in excess of 400° C., typically in excess of 600° C., and at a standard gas hourly space velocity (GHSV) of over 100,000 per hour.
The present invention utilizes chemical looping process layout to prepare a synthesis gas, mainly hydrogen and nitrogen at the right ration, for later conversion to ammonia.
Hydrogen and nitrogen are the two main ingredients used in ammonia synthesis. Hydrogen and nitrogen can be supplied, either separately, where nitrogen from an air separation unit is mixed with hydrogen from a hydrogen unit via hydrocarbon reforming such as steam methane reforming (SMR).
Hydrogen and nitrogen can be produced simultaneously using an air blown auto-thermal reformer for instance where there is no need for an air separation unit.
For small capacities, neither of these technologies are as effective for monetizing production processes using small to medium hydrocarbon feed stocks. Chemical looping where a desulfurized natural gas stream is reacted with steam and pressurized flue gas in a chemical looping reformer before undergoing an isothermal shift and then pressure swing adsorption separation. The resulting synthesis gas is fed to an ammonia synthesis unit where ammonia is produced.
The present invention uses the chemical looping reformer to produce a feedstock of a synthesis gas mixture which is subjected to a shift reaction and separation process to produces hydrogen and nitrogen molecules used in the ammonia production process.